The present invention relates to an in-line type chemical vapor deposition (CVD) apparatus which may be used for producing a thin film transistor(TFT) for a liquid crystal display, or an amorphous Si:H film and SiNx film for a solar battery for example.
It is known that the production of the thin film transistor(TFT) for the liquid crystal display, or the amorphous Si:H film and SiNx film for the solar battery is performed by using a plasma chemical vapor deposition process. Generally, an in-line type plasma chemical vapor deposition apparatus is used as a mass-production system for producing such components. In the conventional in-line type plasma chemical vapor deposition apparatus, a substrate is mounted on a substrate holder under an atmosphere, the substrate holder with the substrate to be processed is introduced into a preparation chamber which in turn is evacuated, and transported into a plasma CVD process chamber in which a thin film is formed on the substrate by the chemical vapor deposition. Then, the holder of the substrate having the thin film formed thereon is carried into a chamber which in turn is vented, and is transported to a taking-out or withdrawing station from which the processed substrate is taken out.
As a practical system there are proposed a vertical type CVD apparatus in which the substrate holder is vertically disposed, a vertical double side type CVD apparatus in which the substrate holder is vertically and movably disposed on the both sides thereof, and a horizontal type apparatus in which the substrate holder is horizontally and movably disposed.
In any one of such conventional apparatuses, at first the substrate to be processed is mounted on the substrate holder which in turn is carried into the preparatory chamber. This preparatory chamber is evacuated by a vacuum pump up to 10.sup.-3 .about.10.sup.-5 Torr. After evacuation of the preparatory chamber, the substrate holder with the substrate is moved into CVD processing chamber. As the case may be, the substrate mounted on the holder may be heated approximately to 200.degree. C..about.300.degree. C. in the preparatory chamber. Into the CVD processing chamber is introduced a gas such as SiH.sub.4, NH.sub.3, N.sub.2 or the like so that a-Si:H film or SiNx film is formed on the substrate. With the plasma CVD process, there is provided a RF cathode electrode opposite to the substrate in the CVD processing chamber. This cathode electrode is supplied with RF voltage for generating a grow discharge to cause the introduced gas to be disolved and to deposit a-Si:H film or SiNx film on the substrate. With the application of a heat assisted CVD or an optical CVD, which will be materialized in the future, the RF cathode is replaced by a heater or a light source for generating a heat or light energy by which the introduced gas is disolved so as to deposit a-Si:H film or SiNx film, or polycrystal Si film or SiO.sub.2 on the substrate.
It is also known to provide a CVD processing chamber having a plurality of chamber sections. For example, if two-layer film consisting of a-Si:H film and SiNx films is to be formed on the substrate, two CVD processing chamber sections may be connected to each other, or there may be provided a separation chamber between the CVD processing chamber sections so that the gases introduced into the respective chamber sections are not mixed.
After the forming of the desired thin film is completed, the substrate holder is transported into the unloading chamber which in turn is vented. Then the substrate holder thus exposed to an atmosphere is returned to the substrate mounting station where a new substrate to be processed is mounted on the returned substrate holder. In this way the above mentioned procedures may be repeated and a plurality of substrate holders may be sequentially moved through the whole system.
With the above mentioned conventional in-line type CVD apparatuses, since the same substrate holder is sequentially and repeatedly used, there is a tendency to deposit a-Si:H film or SiNx film on the holder portion as well as the substrate. In particular, in case of the CVD apparatus for producing the TFT, SiNx film has a thickness of about 5000.ANG. to 10000.ANG. and thus the film to be deposited on the holder portion becomes very thick. Also, the SiNx film has a larger inner stress which causes to peel it off very easily. Consequently, the film deposited on the holder portion may be peeled off easily, which leads to cause any defect on the substrate.
In order to avoid this disadvantage in the conventional apparatuses, as soon as the peeling-off of the undesirably deposited film occurs it is necessary to stop the operation of the system and to clean the inner portion thereof. Therefore, the conventional system has a very low working ratio and a bad yield in the products.
Also, the conventional in-line type CVD apparatuses have another disadvantage that there is an undesirable film deposition on the surface of the cathode and any defect may be formed on the substrate by the peeling-off of the deposited film from the cathode electrode. Since the cathode is in general fixed in the vacuum chamber, the cleaning thereof must be performed by releasing the vacuum chamber from the vacuum condition. As a result, some reduction of the working ratio of the system can not be avoided.
Generally, the films deposited on the substrate holder and the cathode electrode may be removed by a dry-etching which consists of introducing CF.sub.4 or SF.sub.6 into the CVD processing chamber and applying RF voltage to the cathode electrode. However, it is necessary to stop the system for a very long period in order to remove the films deposited on the substrate holder and the cathode with taking time.